The present invention relates to integrated circuit packaging technology, and more specifically, to marking moisture-sensitive devices with labels relevant to dry pack processes.
Due to absorbed moisture, semiconductor devices such as solid state Surface Mount Devices (SMD) could be damaged during solder reflow. The vapor pressure of moisture inside a plastic package of a semiconductor device increases rapidly when the package is exposed to the high temperature of solder reflow. Under certain conditions, this pressure can cause internal delamination of the plastic from the die and/or leadframe, internal cracks that do not extend to the outside of the package, bond damage, wire necking, bond lifting, die lifting, thin film cracking, or cratering beneath the bond. In the most severe case, the stress can result in external package cracks. This is commonly referred to as the xe2x80x9cpopcornxe2x80x9d phenomenon because the internal stress causes the package to buldge and then crack with an audible xe2x80x9cpopxe2x80x9d.
SMDs are more susceptible to this problem then through-hole parts because they are exposed to higher temperatures during reflow soldering. For through-hole devices, the soldering operation occur under the board that shilds the device from the hot solder.
Further, the risk of moisture-induced damage is higher when plastic encapsulation materials are used because plastic is naturally permeable to moisture. The moisture in the package will increase to reach the Relative Humidity (RH) of the surrounding environment.
Controlling the moisture level in the package body is therefore crytical to reducing the risk of moisture-induced damage. To avoid the moisture absorbtion, moisture-sensitive devices are packed in a drypack that consists of desiccant material and a Humidity Indicator Card (HIC) sealed together with the devices inside a moisture barrier bag (MBB). The desiccant material is an absorbent material such as a silica gel used to maintain a low relative humidity in the MBB. The HIC is a card on which a moisture chemical is printed such that it will change color from blue to pink when the preset relative humidity is exceeded.
The IPC/JEDEC J-STD-033 Standard developed by an Institute for Interconnecting and Packaging Electronic Circuits (IPC) and Joint Electronic Device Engineering Council (JEDEC) contains requirements for handling, packing, shipping and use of moisture-sensitive surface mount devices. In particular, this standard requires that a MBB used to pack moisture-sensitive devices should be labeled with a moisture-sensitive caution label. Examples of the moisture-sensitive caution labels are shown in FIG. 1.
The caution label affixed to the outside surface of the MBB varies to reflect the specific product in the bag. The label identifies the contents of the bag and includes the date the bag was sealed, the dry pack expiration date, as well as product handling guidelines.
Also, the caution label contains a moisture-sensitivity (MS) level defined by the IPC/JEDEC J-STD-020A Standard. Moisture-sensitivity levels indicate a time limit for storing a moisture-sensitive device after opening the MBB and prior to mounting the device onto a circuit board, and temperature and humidity to be maintained in storage. The out-of-bag time limit varies depending on the moisture-sensitivity of the product. If the out-of-bag time from initial exposure to board mounting is exceeded, the product should be baked at a prescribed temperature for a prescribed time period.
The IPC/JEDEC J-STD-020A Standard defines six different moisture-sensitivity levels, referred to as level 1 through level 6. Each higher level denotes a higher level of sensitivity. In particular, level 1 corresponds to unlimited exposure time at a temperature not higher than 30xc2x0 C. and relative humidity not higher than 85%. Levels 2, 2a, 3, 4, 5, and 5a require exposure time to be not more than one year, 4 weeks, 168 hours, 72 hours, 48 hours, and 24 hours, respectively. Level 6 is product specific. It directs to follow specific instructions on dry pack label. Levels 2 to 6 prescribe out-of-bag storage at a temperature not higher than 30xc2x0 C. and relative humidity not higher than 60%.
Products are tested to determine their moisture-sensitivity level. Product that fails the level 1 test requirements is then tested at a higher level until it passes. Specific environment stress steps subject the product to conditions designated to simulate the environment of an end-use application. Subsequent electrical testing and inspection steps determine if the device was damaged during the environment stress steps.
Once it is determined that product is moisture sensitive (i.e. it fails the level 1 test), the product is packed in a drypack, and is subject to the dry pack handling procedure prescribed by the IPC/JEDEC J-STD-033 Standard. In particular, a pre-printed caution label is affixed to the outside surface of the drypack to identify the moisture-sensitivity level of the product.
However, labeling of the drypack products is performed manually. As a result, a wrong label can be attached to a drypack. This can cause moisture-induced failure of the device due to incorrect out-of-bag exposure time.
Accordingly, it would be desirable to provide an automatic system for printing correct level caution labels for drypack products, in order to prevent errors during labeling process.
The present invention offers a novel system for automatically generating caution labels for moisture-sensitive semiconductor devices packed in drypack bags. The system comprises a scanner that scans an ID mark representing ID information of a moisture-sensitive device sealed in a drypack bag, and a computing device with a look-up table containing moisture-sensitivity levels assigned to the moisture-sensitive devices. In response to an ID signal produced by the scanner, the computing device searches the look-up table for a moisture-sensitivity level assigned to the packed moisture-sensitive device. The determined moisture-sensitivity level is supplied by the computing device to a label-formatting device for generating a caution label indicating the moisture-sensitivity level. The label-formatting device may control a printer for printing the generated caution label.
In a prefered embodiment of the invention, the moisture-sensitivity levels comply with the IPC/JEDEC J-STD-020A Standard. The look-up table may further comprise information on type of the devices, and lead counts of the devices.
In accordance with a method of the present invention, caution labels are printed automatically when an operator performs labeling of a drypack bag containg a moisture-sensitive device. An ID mark representing ID information of the package sealed in the drypack bag is scanned to produce an ID signal representing the package. Based on the ID signal, a pre-set look-up table is searched for a moisture-sensitivity level assigned to the package. A caution label is automatically generated based on the moisture-sensitivity level found in the look-up table.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.